The overall goal of our program is to develop an imaging technology to assess viscoelastic properties of tissue based on gas bubble dynamics, and, generally, to understand the gas bubble dynamics in viscoelastic medium in the context of several biomedical technologies. Indeed, microbubbles are playing an increasingly important role in biomedical and clinical applications where microbubbles are introduced not only in liquids but also in biological soft tissues. While bubble dynamics in liquid is well understood, the behavior of bubbles in tissue is not. However, such an understanding can lead to the development of novel and improvement of existing biomedical techniques based on how bubbles behave in a viscoelastic medium and how the bubble responds to internal or external excitation. In the current project, we will focus our attention on laser microsurgery of the eye tissue where the bubbles, produced as a result of laser-tissue interaction, are used to cut tissue. The remote, non-invasive, high temporal and spatial resolution, real-time measurements of gas microbubble behavior can be used to image or sense much needed mechanical properties of the eye tissues prior, during and after the surgery. Theoretical, numerical, and experimental studies of gas bubble dynamics in viscoelastic medium are proposed. We will develop a nonlinear model of radial oscillations of a gas bubble in an incompressible elastic medium. The developed model will account for internal gas pressure and the complexity of soft tissue including slight compressibility, tissue viscosity, and tissue elastic heterogeneity and anisotropy. We will also investigate passive bubble dynamics and bubble translational motion and oscillations in response to external excitation such as acoustic radiation force. Next, we will develop ultrasonic and optical techniques capable of measuring the temporal and spatial behavior of the gas bubble. Given these measurements, the algorithms to estimate elasticity (Young's or shear modulus) and viscosity of the tissue surrounding the bubble will be developed. Finally, we will perform laboratory studies to verify our model and to demonstrate the ability of our method to image or sense viscoelasticity of ocular tissues using gas bubble dynamics. Therefore, all theoretical and experimental studies will be conducted to evaluate applicability of the developed methods for ophthalmologic applications.